RNA molecules known as microRNA (miRNA) can influence the expression of target genes. It is thought that mammalian miRNA change the expression of their targets protein while leaving the expression of the cognate mRNA unmodified. [unreadable] [unreadable] These non-protein-encoding miRNA are not only differently expressed but are directly involved in important biological processes such as development and B-cell differentiation. Between 200-255 mammalian miRNA genes are predicted to exist (a number that corresponds to 1 % of all protein encoding genes). Interestingly over 52% of miRNA genes are located in chromosomal fragile sitessome of which are associated with disease. Since each miRNA has the potential to function on several cellular targets their regulatory complexity is potentially enormous. [unreadable] While many of the predicted miRNA have been cloned, the predicted miRNA targets have not yet been evaluated and most mammalian miRNA currently have no identified biological role. [unreadable] We propose to develop the tools that will facilitate the identification of miRNA function and confirm/identify endogenous miRNA targets. We propose to develop a miRNA reporter system, library of miRNA inhibitors and library of miRNA expression vectors or chemically synthesized miRNA corresponding to the known human miRNA. [unreadable] Using these reagents, we will begin to analyze miRNA regulated gene pathways and identify miRNA that participate in a variety of cellular processes, including apoptosis, cell cycle, angiogenesis, proliferation, differentiation, and DNA repair. Combining the resulting data will provide a global view of how miRNA influence human cells and might reveal potential therapeutic targets. [unreadable] [unreadable] [unreadable]